I have a watt meter on the bench supplying my printers (3 of them) , and a room scale air filter system. My kossel Xl draws max 900w when everything is heating up and typically cruises at 200-250w. So 1 hour's printing would be 0.25kwh at 15p/kwh. So around 3.5p/hour. My micro delta can print for 3 hours running from a 16.8v 6600mah lithium pack. Air filter uses between 40-100w depending on fan speed. So I'd say they are pretty low energy consumption and good value unless you're printing yoda heads.

For comparison we think our printers have powerful heaters but my 500w bed uses 1/6 the energy of my kettle! Motors and the like use practically no power at all they are moving really tiny masses very short distances.

However measure the energy consumed by a consumer paper printer and you can see we have a long way to go before we can consider 3d printers A++energy rated appliances.

It would be very interesting to know the energy consumption of an object injection moulded versus 3d printed.